#include <iostream>
#include <cmath>
using namespace std;
#define p 1. / 2. * (a + b + c)

int main()
{
    float a, b, c;
    cin >> a >> b >> c;
    printf("%.1f\n", sqrt(p * (p - a) * (p - b) * (p - c)));
    return 0;
}